Masks are used to supply air or other gas to a patient via his mouth, nose or both. Masks take many different forms but the most common comprises a semi-rigid domed shell shaped to fit around the periphery of both the nose and mouth. The shell usually has some form of softer material around its edge, which provides a seal with the skin surface. An opening in the mask includes a coupling by which the mask is connected to ventilation or anaesthesia equipment. The shell is usually retained in position by means of straps extending around the rear of the patient's head and adjustably fastened to opposite sides of the shell.
There are various problems with existing masks. One problem is that of achieving an effective seal with the contours of the face. Although it is not essential to provide a completely gas-tight seal with the skin surface, if there is not a good fit, gas escaping between the mask and skin can cause discomfort to the patient. Attempts to increase the seal by tightening the straps can increase pressure on the face, which also causes discomfort. Another problem with masks that enclose the nose is that some patients find them claustrophobic. Also, they often prevent the patient wearing spectacles. The straps used to hold the mask on the head can often be difficult to position and adjust correctly. If the mask has to be removed repeatedly to enable access to the patient's mouth it can be time-consuming to have to readjust and reposition the straps of the mask each time it is removed and replaced.
One important use of breathing masks is in CPAP (continuous positive airway pressure) or BIPAP (bidirectional positive airway pressure) ventilation for relieving sleep apnoea by keeping the airways free and open when the muscles of the respiratory tract relax during sleep. In sleep apnoea applications the mask is often worn at home. It is particularly important for such masks to be easy to use and comfortable. Where masks are used in hospitals this is often in intensive care units for patients with heart failure, pulmonary disease or other respiratory problems. CPAP is used to inflate the lungs to a higher functional capacity to allow easier and more effective oxygen transfer.